Piston Pump Having A Force Sensor And A Method For Controlling Said Pump

Abstract

The present invention relates to a piston pump for generating a delivery flow, which is substantially free of pulsation, in particular to a dual piston pump, and to a method for controlling such a piston pump delivering a pumped medium from a low-pressure area into a high-pressure area, wherein measuring sensors detecting mechanical forces or moments transmitted by the structure of the pump or its associated drive unit are used instead of the pressure or flow sensors usually employed for this purpose.

1 . A piston pump for generating a substantially pulsation-free delivery flow of a medium to be delivered, comprising:
 at least first and second piston-cylinder-units for delivering the medium out of a low-pressure area into a high-pressure area;   a drive unit for driving the piston-cylinder units;   a control unit for controlling the driven speed of the drive unit; and   a sensor for collecting an actual value of a control parameter, by which actual value the extent of pulsation of the flow generated in the high-pressure area is derivable;   wherein the sensor is adapted for collecting values of mechanical forces and/or torques exerted or transmitted in or at the structure of at least one piston-cylinder unit and/or the drive unit.   
   
   
       2 . The piston pump of  claim 1 , further comprising:
 an area wetted by the medium being pumped; and   a dry area, which is not wetted by the medium during operation;   wherein the sensor is located in the dry area of the pump and is not wetted by the medium to be delivered.   
   
   
       3 . The piston pump of  claim 1 , wherein the mechanical forces include at least one of tensile stress, compression stress, shear stress and torsional stress. 
   
   
       4 . The piston pump of  claim 1 , wherein the sensor is based on one of a strain gauge, a piezo-electric element, an optical measuring device and an acoustic resonator. 
   
   
       5 . The piston pump of  claim 1 , wherein the piston pump is a parallel dual piston pump. 
   
   
       6 . The piston pump of  claim 1 , wherein the piston pump is a serial dual piston pump. 
   
   
       7 . The piston pump of  claim 1 , wherein each piston-cylinder unit is driven by a separate drive unit. 
   
   
       8 . The piston pump of  claim 1 , wherein each drive unit is driven by a separate motor. 
   
   
       9 . The piston pump of  claim 1 , wherein the first piston-cylinder unit has a suction side in fluid communication with the low-pressure area and a discharge side in fluid communication with the second piston-cylinder unit and the high-pressure area in parallel. 
   
   
       10 . The piston pump of  claim 9 , wherein a discharge side of the second piston-cylinder unit is hydraulically coupled to the high-pressure area. 
   
   
       11 . The piston pump of  claim 9 , wherein the sensor monitors mechanical forces and/or torques being exerted or transferred in or at the structure or drive of the first piston-cylinder unit. 
   
   
       12 . The piston pump according to  claim 11 , further comprising an additional sensor configured to monitor mechanical forces and/or torques being exerted or transmitted in or at the structure or drive of the second piston-cylinder unit. 
   
   
       13 . The piston pump of  claim 1 , wherein the drive unit is designed to generate a pre-compression stroke. 
   
   
       14 . The piston pump of  claim 1 , wherein the drive unit comprises a cam drive. 
   
   
       15 . A method for controlling a piston pump for delivering a medium out of a low-pressure-area into a high-pressure-area, the piston pump including at least first and second piston-cylinder units, a drive unit for driving at least one of the piston-cylinder-units, and a sensor for monitoring mechanical forces and/or torques exerted or transmitted in or at the structure of at least one of the piston-cylinder units and/or said drive unit, comprising:
 i) driving at least one piston-cylinder unit by a drive unit at a first speed (n), and monitoring using the sensor mechanical forces and/or torques exerted or transmitted in or at the structure of the at least one driven piston-cylinder unit and/or the drive unit;   ii) monitoring the moment of the actual onset of delivery of the pumped medium out of the at least one driven piston-cylinder unit into the high-pressure-area by using the values of the mechanical forces and/or torques monitored by the sensor;   iii) monitoring the rate of compression of the pumped medium at the moment of the actual onset of delivery;   iv) modulating the drive unit rotational speed to a second speed (n+1), such that a varying compression rate due to varying system back pressure and/or varying compressibility of the pumped medium arising on the high-pressure side of the at least one driven piston-cylinder unit is compensated and a substantially pulse-free delivery flow of the pumped medium is generated in the high-pressure area and   v) repeating steps i) to iv) for each pumping cycle using the drive unit rotational speed (n+1) modulated in step iv) as the first speed (n).   
   
   
       16 . The method of  claim 15 , wherein in step ii) the variation of the values measured for the mechanical forces and/or torques is monitored. 
   
   
       17 . The method of  claim 15 , wherein the mechanical forces and/or torques or the course of their measuring values in step ii) are monitored during a single pump stroke at constant drive unit rotational speed. 
   
   
       18 . The method of  claim 15 , wherein stored running programs are used for modulation of the drive unit rotational speed. 
   
   
       19 . The method of  claim 18 , wherein a correction factor is derived based on the actual onset of delivery and wherein a specific rotational speed control program is selected depending on the correction factor. 
   
   
       20 . The method of  claim 15 , wherein in step i) a rotational speed control program is applied, which is tuned to the flow rate set at the piston pump. 
   
   
       21 . The method of  claim 15 , wherein the medium being pumped is pre-compressed at the beginning of each pumping cycle. 
   
   
       22 . The method of  claim 21 , wherein a secondary correction factor is superimposed onto the drive unit rotational speed which compensates for the excess delivery flow referred to volume at ambient pressure generated by the precompression. 
   
   
       23 . The method of  claim 21 , wherein the pre-compression stroke is adapted to a specified maximum delivery pressure and a maximum specific compressibility to be expected for the pumped medium. 
   
   
       24 . The method of  claim 21 , wherein the drive unit rotational speed is reduced when being modulated during the pre-compression stroke. 
   
   
       25 . The method of  claim 15 , wherein the composition of medium to be delivered by the pump varies over time. 
   
   
       26 . The method of  claim 15  wherein a volume which cannot be expelled from the displacement area of the piston-cylinder unit of the working piston as detrimental dead volume, but still has to be compressed according to current operation conditions before actual pumping can onset, is monitored for each pumping cycle in order to determine the loss of filling efficiency due to expansion of said volume at the beginning of the suction stroke. 
   
   
       27 . The method of  claim 25 , wherein the gradient composition for the subsequent filling stroke is corrected according to the expansion of the not dischargeable detrimental dead volume within the displacement area of the first piston-cylinder unit. 
   
   
       28 . The method of  claim 15 , wherein the drive unit comprises a cam drive.